Cook the spaghetti according to package directions.
Drain and set aside.
Melt butter in a heavy saucepan over medium heat.
Saute the onion until it begins to soften, then add the garlic.
Cook about a minute stirring often, or until garlic is soft. Don’t let it scorch!
Whisk in cream of chicken soup, cream cheese, milk, and 1 cup of the cheese mixture.
Heat, stirring constantly until the cheese melts.
Add the ham and pimentos.
Stir in the spaghetti.
Spoon into the prepared casserole dish.
Cover with aluminum foil and bake for 20 minutes.
Uncover, sprinkle with remaining cheese mixture and fried onions.
Bake for 5 to 10 more minutes, or until cheese is melted.
Sprinkle with parsley before serving.
Notes
Storage:Once the baking dish has cooled down, cover it tightly with plastic wrap or spoon the leftovers into an airtight container. They'll last in the refrigerator for a few days.Leftover cooked ham, by itself, has a storage "shelf life" of up to five days. Recooking the ham doesn't reset that amount of time. So, keep in mind that if you use leftover ham in the tetrazzini, your casserole leftovers will only keep for as many days as the ham has left.To reheat:To reheat the classic comfort food dish, bake it, covered, at 350 degrees F, or warm it up in the microwave until it meets your liking. You could heat it on top of the stove over medium heat, but the crunchy onions will lose their crispiness.Tips:
If you don't have any leftover ham use a precooked ham steak. You can also buy deli-meat ham from the grocery store—just ask them to cut a few slices, each about a half-inch thick.
Don't overcook the pasta or it'll be mushy after baking. The noodles will absorb a little moisture from the creamy cheese sauce while in the oven.
Let the onions and garlic get nice and browned—but not burnt. If you have time, you can let them caramelize. That'll give extra deep flavor to the rich, creamy sauce.
If your casserole dish is very full, place it on a baking sheet before putting it in the oven. It's easier to transport, and will also help catch any drips if your casserole gets too bubbly while cooking!
Coat the underside of the aluminum foil with non-stick cooking spray to prevent it from sticking to the cheese when reheating the casserole.
You can make the ham tetrazzini a day or two in advance, refrigerating in the meantime. Assemble it as written and cover tightly, but leave off the onions and cheese topping. Before putting it in the oven, be sure to let it sit at room temperature for about 30 minutes. Cold glass in a piping-hot oven has a tendency to crack!